The invention relates to a plate-like electrostatic actuator which comprises at least one plate-like stator with an electrode formed on its surface and at least one moving diaphragm, and in which a signal is transmitted to the electrode along a signal line.
The invention further relates to a method for directing the sound field of a plate-like electrostatic actuator which comprises at least one plate-like stator with an electrode formed on its surface and at least one moving diaphragm, and in which a signal is transmitted to the electrode along a signal line.
Today, the directing of a radiation sound field is typically implemented by forming several sound sources and feeding a signal to each sound source by using a different delay and/or signal amplitude. The delay and frequency filtration of the signal is established by using either a constant-value or adjustable RC circuit, or alternatively by multi-channel analogue or digital signal processing. The use of several sound sources requires several delay circuits, and it is possibly necessary to use several amplification channels. Therefore, the system becomes complex and the number of required components large.
Publication U.S. Pat. No. 4,338,489 discloses a structure used mainly in headsets for directing the radiation field of an actuator. In this solution, the sound-producing diaphragm is divided into several sections and a signal directed to the different sections is delayed differently. Publication JP 2 265 400 discloses a solution for adjusting the directivity of a loudspeaker. In this solution, a large number of vibrators are arranged on the same plane, and the signal coming to each vibrator is directed through its own delay device. Directivity is provided by adjusting the phase delay angles of the delay devices appropriately. Both solutions do, however, require separate delay devices or circuits for forming the delay for different parts of the diaphragm or separate vibrators, which increases the number of components and the complexity of the system.